1. Field of the Invention
This invention relates to fiber optic devices for coupling signals to and from fiber optic cables used for the transmission of digital and analog data. In particular, this invention relates to a Wavelength Division Multiplexer (WDM) multiplexing and demultiplexing fiber optic switch and coupler useful for interconnecting processors at various sites linked by an optical fiber and to distributed processor systems configured therefrom.
2. Description of the Prior Art
Conventional optical couplers use various techniques for coupling one or more channels of signal information to and between fiber optic waveguides.
Maltenfort, in "Integrated Optic Wavelength-Division Multiplexing System for Optical Fiber Communication Systems", Proceedings of the SPIE, vol. 704, pp. 152-159, 1986, proposes a WDM design using waveguide lenses and a diffraction grating to permit multiple channel coupling. In the demultiplexing mode, optical energy including multiple wavelengths of light are applied from a fiber optic waveguide at an angle to a planar periodic diffraction grating used as a dispersive element. The different wavelengths are thereby separately focused on each of a series of photodetectors in an array. In the multiplexing mode, light of different wavelengths from an array of LED's is focused on the diffraction grating so that the combined result may be applied to the fiber optic waveguide.
Laude, Gautherin, Philips and Lerner, in "High-performance eight-channel multiplexer/demultiplexer for monomode fibers," Technical Digest of the Conference on Lasers and Electro-Optics, paper THK20, pp. 288-289, 1986 describes a WDM optic coupler using a diffraction grating and concave mirror. In the demultiplexing function, the light from a single fiber optic waveguide is separated by the diffraction grating into its component wavelengths which are then applied by the concave mirror to the appropriate one of eight output waveguides. The multiplexing function operates the system in reverse.
Katoh, Tachikawa, Oguchi and Fujii, in "Three-channel wavelength-division-multiplexing transceiver module assembled without an adjustment process", ibid., paper THS5, pp. 332-333, proposes an easy to assemble WDM micro-optic device using a glass block with interference filters to separate light of different wavelengths to or from a lens terminated fiber optic waveguide.
Kazarinov, Henry and Olsson, in "Narrow-Band Resonant Optical Reflectors and Resonant Optical Transformers for Laser Stabilization and Wavelength Division Multiplexing," IEEE Journal of Quantum Electronics, vol QE-23, no. 9, pp. 1419-1425, 1987, propose a WDM optic coupler in which a high-Q, distributed BRAGG resonator is coupled between a pair of waveguides in an integrated optical circuit to inject many closely spaced wavelength signals into a single waveguide.
Alferness and Buhl, in "Tunable electro-optic waveguide TE&lt;-&gt;TM converter/wavelength filter", Applied Physics Letters, vol. 40, pp. 861-862, 1982 report an electrically tunable integrated electro-optic circuit wavelength filter and propose its utility for WDM optic devices.
Kondo, Miyazaki and Akao, in "Optical Tunable Switched Directional Couplers Consisting of Two Thin-Film Waveguides Using Surface Acoustic Waves", Japanese Journal of Applied Physics, vol. 17, No. 7, pp. 1231-1243, July 1978, analyze the effect of a Surface Acoustic Wave (SAW) on the coupling of optical power between parallel thin film planar waveguides in an acousto-optic tunable switched directional coupler. The optical center wavelength of the controllable range can be tuned by the SAW frequency and the fraction of the optical power transferred can be controlled by adjusting the SAW amplitude for different optical wavelengths independently. The switched directional couplers using SAW's discussed in this paper are proposed for application in tunable lasers, tunable filters or optical wave separators in integrated optic devices and would be useful in WDM technology.
None of the conventional devices combine the necessary characteristics for a WDM optic coupler in a large, distributed processor multiprocessor computer system linked by a common fiber optic path.
The desired device would provide high density multiplexing to maximize the system's data handling capacity by providing a channel for each of the hundreds of processors potentially connected to a large system. The desired device would also provide bidirectional, independent, multichannel interfacing capabilities at each site and be capable of convenient assignment and reassignment of both transmit and receive wavelengths.
The required interface should also be capable of a transparent failure mode, that is, in the event of a failure of any given interface, data transmission on the fiber as well as the bidirectional coupling of the other interface devices on the system would not be interrupted.